Thermoplastic and thermoset main chain liquid crystal polymers prepared from biphenyl mesogen

Main chain liquid crystal thermoplastic polyesters and thermosetting epoxy resins were prepared using biphenyl mesogens. The melting points of the polyesters were effectively decreased by incorporating flexible methylene spacers into the polymer main chain. The liquid crystal epoxy resins exhibit high glass transition temperature, low thermal expansion coefficients, high dielectric strengths, and low dielectric loss. They are suitable for the preparation of self-reinforcing molecular composites. © 1993 John Wiley & Sons, Inc.     

Qualification of automated low-field NMR relaxometry for quality control of polymers in a production setting

Implementation of a low-field time-domain nuclear magnetic resonance (NMR) scanner as a diagnostic tool in the production of new polymer components is described in the context of qualification of a new QA/QC device. A study to determine the optimal experimental parameters was performed and a robotic autosampler was built to enable scanning of multiple pads. Relationships between T₂ values and physical properties of DC745 slabs were investigated, and the appropriate sampling parameters for the production setting were determined. Two versions of a robotic autosampler were built and, for the component described here, a fourth radial axis was required in addition to traditional X, Y, and Z movement to eliminate the large variability in T₂ due to inconsistent sample coverage caused by the complex rib geometry of the component. Data show that with appropriate choice of experimental conditions of the NMR detector and the detection geometry of the robotic autosampler, sufficient resolution of variations in cross-link density on the millimeter scale could be determined. All data to date demonstrate that low-field NMR devices are a feasible tool for use in production settings for non-destructive quality control of polymer components.     

Thermoplastic fusion bonding using a pressure-assisted boiling point control system

A novel thermoplastic fusion bonding method using a pressure-assisted boiling point (PABP) control system was developed to apply precise temperatures and pressures during bonding. Hot embossed polymethyl methacrylate (PMMA) components containing microchannels were sealed using the PABP system. Very low aspect ratio structures (AR = 1/100, 10 μm in depth and 1000 μm in width) were successfully sealed without collapse or deformation. The integrity and strength of the bonds on the sealed PMMA devices were evaluated using leakage and rupture tests; no leaks were detected and failure during the rupture tests occurred at pressures greater than 496 kPa. The PABP system was used to seal 3D shaped flexible PMMA devices successfully.     

Thermoplastic polymers: overview of several properties and their consequences in flax fibre reinforced composites

In order to assess the most suitable thermoplastic polymer for a certain application, one must know the properties of the available polymers. Since data tend to be widely scattered over many sources, it is the purpose of this article to give an overview of the most relevant properties of a range of thermoplastic polymers. The reported properties are divided into mechanical, physical, and thermal ones. It is clear that many of these properties are interrelated. By consequence some combinations of desired properties are not possible but an overview such as this may provide a useful guide in establishing the best compromise between conflicting property demands. Data are presented mostly as ranges (in tables) as well as in graphs for quick comparison reasons. One specific application (thermoplastic pultrusion with flax as reinforcement) is also studied. In this particular case, polypropylene is found to have the best combination of properties in order to be used as the composite matrix.     

Electroactive conducting polymers for corrosion control

This paper reviews the literature describing the effects of conducting polymer coatings on the corrosion rate of ferrous alloys (iron, steel and stainless steel). The literature is interpreted in terms of the proposed mechanisms of corrosion protection: barrier, inhibitor, anodic protection and the mediation of oxygen reduction. The most intriguing aspect of the reported literature are the studies demonstrating corrosion protection when deliberate defects were introduced into the coating to expose the bare metal. These studies show that protection afforded by conducting polymer coatings is not due to simple barrier protection or inhibition alone. Many studies illustrate that the polymer/metal interface is modified to produce passivating oxide layers and that charge transfer reactions occur between the metal and polymer. These studies support the proposed anodic protection mechanism, as do the reports of significant ennoblism. On the other hand, there is considerable variation in the reported shift in corrosion potential and these highlight the influence of substrate preparation, coating composition and mode of application and the nature of the electrolyte on the corrosion protection provided by the conducting polymer. For example, the evidence suggests that the emeraldine base form of polyaniline is superior to the emeraldine salt in terms of corrosion protection for steel. However, the number of direct comparisons is small and the reasons for the differences are not well understood. Also not well understood are the role of the counterion release and local pH changes on pinhole protection. It is also argued that the conducting polymer reduces the likelihood of large increases in pH at the polymer/metal interface and so stabilizes the coating against cathodic disbondment. Further work is clearly needed to increase the protection period by further studies on the corrosion protection mechanism so that the polymer composition and processing methods may be optimized.     

Electroactive conducting polymers for corrosion control

There is an intensive effort underway to develop new corrosion control coatings for structural metals. In part, this effort has been motivated by the desire to replace chromium(VI)-containing coatings currently used for corrosion control of iron and aluminum alloys. Cr(VI) has been shown to be hazardous to the environmental and to human health, and its use in many countries will be sharply curtailed in the coming years. Electroactive conducting polymers (ECPs) represent a class of interesting materials currently being explored for use in corrosion control coating systems, possibly as a replacement for Cr(VI)-based coatings. The electroactivity and the electronic conductivity (or semiconductivity) of ECPs set them apart from traditional organic coatings. As with chromate, interesting and potentially beneficial interactions of ECPs with active metal alloys such as steel and aluminum are anticipated, with concomitant alteration of their corrosion behavior. A review of this active research area will be presented in two parts. Here in Part 1, a general introduction to the topic of corrosion control by ECPs will be presented, including an overview of corrosion and its control by traditional methods, an introduction to ECPs and their properties, and a discussion of the processing issues surrounding the use of ECPs as coatings. Part 1 also includes a review of the literature on the use of ECPs as coatings (or components of coatings) on non-ferrous active metals, principally aluminum and aluminum alloys, although some work on zinc, copper, silver, titanium and silicon will also be described. In Part 2 of this review (to be published in the next issue of this journal), the rather extensive literature on the use of ECPs for the corrosion control of ferrous alloys (steels) will be reviewed. Electronic Publication     

Thermoplastic Starch

The thermoplastics processing of native starch in the presence of water is a recent development with very wide possible applications. Eventually, oil-based polymer materials have to be replaced in many applications by sustainable, inexpensive, natural materials from renewable resources. The present contribution focuses on the injection moulding of starch. The bases of the processing and the thermal and molecular changes occurring are described. In addition, the rheological behaviour of starch-water melts during processing is analysed quantitatively to give apparent melt viscosities. The dimensional, thermal and mechanical properties of moulded thermoplastic starch polymer (TSP) materials and the products presently being produced from them are discussed.     

Structural rigidity control in arborescent graft polymers

Successive chloromethylation-anionic grafting sequences on polystyrene have led to well-defined hyperbranched macromolecules. Polymers with branching functionalities f > 5000 and molar masses over 10⁷ g/mol were thus prepared while maintaining a ratio of mass- to number-average molar masses M_w/M_n = 1,1-1,3. Three series of styrene polymers were prepared by varying the density of grafting sites along the chain, resulting in controllable stiffening of the molecular structure. Characterization of the branched molecules by size-exclusion chromatography/low-angle laser light scattering and light scattering confirmed a geometric increase in molar mass for successive generations, and a low ratio of mass- to number-average molar masses. Static and dynamic light scattering experiments showed that the molecules behave like hard spheres in dilute solutions. Measurements in the semidilute range, however, showed a progressive structural stiffening effect as the branching density increases.     

Collaborative study to improve the quality control of trace element determinations in polymers. Part 1. Interlaboratory study

In order to control the quality of trace element determinations in polymer, the Standards, Measurements and Testing Programme (formerly BCR) of the European Commission has started a project of which the final aim is to certify polymer reference materials for their contents of a range of trace elements. The first part of this project consisted in an interlaboratory study which aimed at testing the feasibility of preparation of candidate polymer reference materials and to detect and remove most of the pitfalls observed in trace element determinations. This paper presents the results of this interlaboratory study carried out prior to the certification campaign. Received: 22 April 1999 / Revised: 21 June 1999 / Accepted: 21 June 1999     

Collaborative study to improve the quality control of trace element determinations in polymers. Part 1. Interlaboratory study

In order to control the quality of trace element determinations in polymer, the Standards, Measurements and Testing Programme (formerly BCR) of the European Commission has started a project of which the final aim is to certify polymer reference materials for their contents of a range of trace elements. The first part of this project consisted in an interlaboratory study which aimed at testing the feasibility of preparation of candidate polymer reference materials and to detect and remove most of the pitfalls observed in trace element determinations. This paper presents the results of this interlaboratory study carried out prior to the certification campaign. Received: 22 April 1999 / Revised: 21 June 1999 / Accepted: 21 June 1999     

Thermoplastic amphiphilic conetworks

Our main objective was the design, synthesis, characterization, and testing of a novel class of materials, thermoplastic amphiphilic conetworks (TP‐APCNs). A further objective was the evaluation of TP‐APCNs as biomaterials, for example, as immunoisolatory membranes in a bioartificial pancreas, or as extended‐wear soft contact lenses. The synthesis of the first TP‐APCNs was accomplished by blending an amphiphilic graft polymer, poly(dimethyl acryl amide)‐g‐polydimethylsiloxane (PDMAAm‐g‐PDMS), with a commercial PDMS‐containing polyurethane (PU). The common PDMS segments coalesce and form a single phase, whereas the hard/crystalline segments of the PU physically crosslink the blend. The properties of TP‐APCNs can be controlled by the graft/PU ratio and segment molecular weights. TP‐APCNs with cocontinuous hydrophilic and hydrophobic phases were prepared as demonstrated by swelling in water and n‐heptane. Depending on the blend ratio and molecular weights, optically clear water‐swollen TP‐APCNs with 0.5–4 MPa tensile strength, 70–280% elongation, together with 2–11 × 10^?7 cm²/s glucose permeability, and 1.2–8 × 10^?8 cm²/s insulin permeability were prepared. TP‐APCNs are processible by casting and molding. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 682–691, 2009     

Uncertainty-based measurement quality control

According to a simple acceptance decision rule for measurement quality control, a measured value will be accepted if the expanded uncertainty of the measurements is not greater than a preset maximum permissible uncertainty. Otherwise, the measured value will be rejected. The expanded uncertainty may be calculated as the z-based uncertainty (the half-width of the z-interval) when the measurement population standard deviation σ is known or the sample size is large (30 or greater), or by a sample-based uncertainty estimator when σ is unknown and the sample size is small. The decision made based on the z-based uncertainty will be deterministic and may be assumed to be correct. However, the decision made based on a sample-based uncertainty estimator will be uncertain. This paper develops the mathematical formulations for computing the probability of acceptance for two sample-based uncertainty estimators: the t-based uncertainty (the half-width of the t-interval) and an unbiased uncertainty estimator. The risk of incorrect decision-making, in terms of the false acceptance probability and false rejection probability, is derived from the probability of acceptance. The theoretical analyses indicate that the t-based uncertainty may result in significantly high false rejection probability when the sample size is very small (especially for samples of size 2). For some applications, the unbiased uncertainty estimator may be superior to the t-based uncertainty for measurement quality control. Several examples from acoustic Doppler current profiler streamflow measurements are presented to demonstrate the performance of the t-based uncertainty and the unbiased uncertainty estimator.     

A proficiency test scheme for the quality control of black tea and development of quality control material for internal quality control

A proficiency test (PT) was organized for quality control analysis of black tea. Test materials for the analyses of total content of powder tea, moisture, total ash, acid-insoluble ash, water-soluble ash, alkalinity of water-soluble ash, water extract, crude fiber and caffeine were sent to the participant laboratories (n:43) in 2009. The assigned value, standard deviation of the parameters and z-scores of the participant laboratories were calculated using the data reported by the participants. The percentage of the reported results for analytes was found to be ranged from 67.5 to 100%. Acceptable z-scores were achieved by 80.5–97.5% of the participant laboratories. More than 15% of unacceptable results were obtained for acid-insoluble ash and caffeine analyses. The quality control material for quality control analysis of black tea was developed from the remaining material.     

Conformational control in the cyclization of hydrogen-bonded supramolecular polymers

Bifunctional 2-ureido-4[1H]-pyrimidinone (UPy) derivatives can form small cyclic oligomers as well as long supramolecular polymers in chloroform solutions using the quadruple hydrogen-bonding motif. Ring-chain equilibria of a set of supramolecular monomers containing methyl-substituted alkyl linkers between the hydrogen-bonding UPy moieties were investigated by (1)H NMR spectroscopy and viscometry. The data were characterized in terms of critical concentration (CC, denoting the onset of polymerization) and equilibrium cyclic dimer concentration (EDC, representing preorganization of the monomer toward selective formation of cyclic dimer). Methyl substituents in the monomer were found to promote conformations favorable for cyclic dimerization, leading to an increase in both the EDC and the CC with respect to unsubstituted monomer. Furthermore, we observed an odd-even effect in the CC and EDC with increasing length of the linker between the hydrogen-bonding units. The combined results allow tuning of the critical concentration over a broad range and offer detailed information on the correlation between monomer structure, conformation, and polymerizability which may provide new insights for the study and design of other ring-chain equilibria or helix-random coil transitions.     

Wide control of proton conductivity in porous coordination polymers

The proton conductivities of the porous coordination polymers M(OH)(bdc-R) [H(2)bdc = 1,4-benzenedicarboxylic acid; M = Al, Fe; R = H, NH(2), OH, (COOH)(2)] were investigated under humid conditions. Good correlations among pK(a), proton conductivity, and activation energy were observed. Fe(OH)(bdc-(COOH)(2)), having carboxy group and the lowest pK(a), showed the highest proton conductivity and the lowest activation energy in this system. This is the first example in which proton conductivity has been widely controlled by substitution of ligand functional groups in an isostructural series.